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Old 08-01-2020, 12:05 PM   #1
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Solar controller

Solar controller question.
I know that you’re supposed to Connect the battery on your controller before you powder the panels to it my question is if there’s a fuse past the controller to the batteries and it blows what happens to the controller having the panels connected. The directions explicitly says to power it first and reverse order to powering down to work on it
My plan was to fuse (breaker)before and after the controller
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Old 08-01-2020, 12:24 PM   #2
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Not a solar expert but the issue happens if the open circuit voltage from the panels is greater than what the controller can handle. See what you panels open circuit voltage is and what your controller can handle.
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Old 08-01-2020, 12:26 PM   #3
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open circuit voltage from the panels is greater than what the controller can handle.
if this is the case, and it sounds like it, I doubt that a fuse in the circuit will blow in time to protect anything
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Old 08-01-2020, 12:41 PM   #4
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Not a solar expert but the issue happens if the open circuit voltage from the panels is greater than what the controller can handle. See what you panels open circuit voltage is and what your controller can handle.

If that happens then the panels are not wired correctly or the controller is not properly sized.

If all panel's Vmax rating, wired in series, series/parallel, or parallel only don't exceed the Vmax rating of the controller that shouldn't be an issue.

On my small solar setup my controller is wired directly to the Positive Bus and there is a 100 amp fuse and shutoff switch inline to the battery. Switch is always on with no reason to turn it off when solar is connected. Fuse is for current draw on batteries and very unlikely to blow from solar panel output. My Controller has it's own fuse.

Solar output on mine is "switched" by my plugging/unplugging solar suitcase but no different than if one has a switch/circuit breaker on their panel output from roof mounted.

If one disconnects the Panels first and battery second when servicing I see no problems. Battery first when reconnecting is only logical.
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Old 08-01-2020, 12:57 PM   #5
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Not a solar expert but the issue happens if the open circuit voltage from the panels is greater than what the controller can handle. See what you panels open circuit voltage is and what your controller can handle.
Definitely have to have the OC voltage less than the spec for the PV input of the controller.



The issue with connecting the PV array before the battery is that on some controllers, its output voltage will rise too high since there is no load and burn out its output. Many controllers don't have this issue but some of the cheaper ones will.


Also, some controllers auto sense if the battery bank is 12V or 24V. If you had the controller hooked to the RV and the battery was disconnected, you could possibly power the RV with 24V from the controller which would be a very bad thing with a 12V system RV.
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Old 08-01-2020, 03:13 PM   #6
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Definitely have to have the OC voltage less than the spec for the PV input of the controller.



The issue with connecting the PV array before the battery is that on some controllers, its output voltage will rise too high since there is no load and burn out its output. Many controllers don't have this issue but some of the cheaper ones will.


Also, some controllers auto sense if the battery bank is 12V or 24V. If you had the controller hooked to the RV and the battery was disconnected, you could possibly power the RV with 24V from the controller which would be a very bad thing with a 12V system RV.

Victron guards against that once initial setup is complete. Starts up on that first setting each time thereafter and auto sense is disabled.

You'd think that any auto sense would start on lowest voltage unless it detected a higher voltage on the battery connection.

One more reason to avoid "cheap" if possible.
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Old 08-01-2020, 05:08 PM   #7
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I have the EPEVER TRIRON 2210N 20 amps
Only two 100 watt panels wiring them for 12 volts. It sounds like I should not have any problems
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Old 08-01-2020, 06:45 PM   #8
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I have the EPEVER TRIRON 2210N 20 amps
Only two 100 watt panels wiring them for 12 volts. It sounds like I should not have any problems
I have a couple of their 10A controllers I use with 50W panels to keep batteries topped off on one of my boats and truck. The panels are permanently attached to the panel so sometimes they are outputting without the battery load on it.



Why not wire your panels in series? Less voltage drop in the wires going to the controller that way. Also, will start outputting in lower light than panels in parallel.
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Old 08-02-2020, 06:00 PM   #9
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I have the EPEVER TRIRON 2210N 20 amps
Only two 100 watt panels wiring them for 12 volts. It sounds like I should not have any problems
In addition to efficiency already mentioned, you have an MPPT controller that works best if it has some headroom between the solar and battery voltages. With the panels in series the controller starts with a higher voltage and can do more to extract power at lower sun angles. It also can fail to find the maximum power point if there is not some headroom.
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Old 08-03-2020, 11:42 AM   #10
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Can you explain the Failure to fine maximum PowerPoint if there’s no headroom
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Old 08-03-2020, 02:28 PM   #11
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Can you explain the Failure to fine maximum PowerPoint if there’s no headroom
Sure. Here's what I know about them. Much of this is from my Epever solar controller manual.

The controller needs a solar panel voltage a volt or two above the battery voltage to even engage its MPP algorithm. The OP's "12 volt" panels may not have sufficient open circuit voltage, at least when the sun is low, to trigger the MPPT algorithm.

At lower sun angles the MPP may be at 1/3 or less of the panel's open circuit voltage. If the OP's panels are, say, 18 volt open circuit, and the MPPT controller can't go below 15 volts input, it's often not going to get voltage down to an MPP, and maybe only doing so near max sun.

I don't know what the open circuit voltage of the OP's parallel "12 Volt" panels is, but presumably it's not up around the 25-40V where 12V solar controllers work best. My Epever solar controllers suggest panels totaling about 30V to be optimum with twice that being maximum for good performance.

If the controller can't find an operating point it will default to some voltage below the panel open circuit voltage and above the battery voltage (plus the minimum volt or two of converter voltage drop), possibly far from optimum.

The other issue is that there are often two maximum power points at very different voltages. I'm thinking one is better at high sun and the other at lower sun, but haven't seen this demonstrated. Given only a narrow range of voltage to work in, it's likely only one MPP exists (or none) so a possible higher one isn't available.

From an MPPT standpoint, the OP definitely will be better off with his two "12 volt" panels in series.

Another problem is that efficiency drops as the input voltage rises. There is more energy loss when chewing up a higher DC voltage and spitting out the 12-14V battery DC voltage. My Epever losses are a couple percent higher at 66V input than at 33V input. Too high of a voltage isn't a problem for the OP, but I mention it because it is a reason to do series-parallel panels to get 30-40 volts, high enough to have good MPP performance and not so high that controller losses increase.
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Old 08-04-2020, 07:38 PM   #12
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Thanks.
OC 21.3 V on the panels
Control. 260w (12v),520w(24v) Max PV 100v

A was a little concerned about shade and taking out both panels power. my understanding is if their wired and series, shade on one panel would lose both. Wired in parallel you could lose one panel and still have the other one producing power But I guess my real question is with the OC at 21.3 V each what’s the safest for the controller to be wired ,12 volts are 24. I’m pretty open to either way just trying to make sure I keep controller from Burning out if for some reason the battery got disconnected.
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Old 08-05-2020, 01:11 AM   #13
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Thanks.
OC 21.3 V on the panels
Control. 260w (12v),520w(24v) Max PV 100v

A was a little concerned about shade and taking out both panels power. my understanding is if their wired and series, shade on one panel would lose both. Wired in parallel you could lose one panel and still have the other one producing power But I guess my real question is with the OC at 21.3 V each what’s the safest for the controller to be wired ,12 volts are 24. I’m pretty open to either way just trying to make sure I keep controller from Burning out if for some reason the battery got disconnected.
You mention "12 volts or 24" .... if you are thinking panel voltage, the voltages of interest are 21.3 (parallel) or 42.6 (series). If by 12 or 24 you are looking at the solar controller voltage selection setting, that setting applies to your battery voltage. Some RVs have 24V systems but most are 12V. Yours is 12V so the solar controller should be set for 12V. Or set it on Auto if it has that option. In Auto, it will test the battery voltage and set itself appropriately each time it boots up.

Re the panels; you are correct that the panels in parallel will perform better than series if one is shaded. If one panel is heavily shaded, there won't be much advantage to parallel. If one panel is partially shaded, parallel will do somewhat better.

However, 21.3V open circuit from parallel panels means an operating voltage around 18 or 19V at the MPP when the sun is good. That's enough headroom for a decent solar controller, when there is good sun. With weak sun or early morning or late afternoon sun the MPP will be too low for the controller to reach it (below about 15V). Series, on the other hand, with 42.6V open circuit and a typical good-sun operating point up around 35V will provide plenty of headroom even with weak sun or early or late day operation.

Yes, you will be moving the panels to face the sun. But even then, the sun is further away and passing through more atmosphere and will be weaker, so series is more likely to let the controller find a MPP. And, with series, it will be less critical to reorient the panels often.

And, you reduce losses in the wires by a few watts by going series thereby halving the current (think I squared R, so wire losses are cut by a factor of four when the voltage is doubled and current is halved).

If it were me, I'd go series. I think it will provide measurably more power, especially when the sun is weak due to clouds, haze, or time of day.

If you will be in shade often, and only one panel will be shaded, and maximizing power under that condition is very important, then parallel may be best. But, series will be considerably better than parallel if both panels are partially shaded.

Do check for diodes. They are usually in a black box on the back of the panel where the wires come out. That box is about 2.5" x 2.5" by 0.5" thick. Don't try to open this box, but if it's there the panels surely have diodes. If you have the specs for the panels, that should mention diodes if they exist. Even without diodes, I'd go series.

You could test both modes under some condition that you expect to have often. But, unless you have a one-panel-shaded condition often, then series will be significantly better.
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Old 08-05-2020, 01:56 AM   #14
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Solar controller question.
I know that you’re supposed to Connect the battery on your controller before you powder the panels to it my question is if there’s a fuse past the controller to the batteries and it blows what happens to the controller having the panels connected. The directions explicitly says to power it first and reverse order to powering down to work on it
My plan was to fuse (breaker)before and after the controller
If the fuse past the controller is sized properly and healthy (they do wear out), then it should only blow if there's a fault in the controller. If there's a fault in the controller, having the controller remain connected to the panel isn't a hazard to the controller. It's shot anyway.

Though depending on where in the controller the fault is, the panels may put some energy into the fault thus possibly continuing the smoke and arcing after the battery side fuse has blown. There's nothing to be done about this risk. The fault current from the panel(s) will be too low to operate any protection you could put between the panel and the controller (that protection must pass MPP current which will be higher). This is a small risk, not one to worry about.
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Old 08-05-2020, 09:40 AM   #15
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Thanks, that was great information and you’ve help me out quite a bit,. Going with your recommendations. thanks again
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Old 08-05-2020, 10:36 AM   #16
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A Victron MPPT needs 5v headroom to even start. States this in their manuals.

The controllers are actually more efficient with a higher input voltage.

An MPPT controller is essentially a DC to DC converter. It is more efficient the higher the input voltage is.

Is is always more advantageous to have 4 panels in series vs 2 serial and 2 parallel. Problem is that most controllers can't handle the input voltage and when you get above 48v, it's a little harder to find switches and breakers to handle the higher voltage.

If your panels do not have bypass diodes, you almost have to go parallel. With no bypass diodes, shade on just one panel will drop the output of your entire PV string to zero.
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Old 08-05-2020, 08:06 PM   #17
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A Victron MPPT needs 5v headroom to even start. States this in their manuals.

The controllers are actually more efficient with a higher input voltage.

An MPPT controller is essentially a DC to DC converter. It is more efficient the higher the input voltage is.

Is is always more advantageous to have 4 panels in series vs 2 serial and 2 parallel. Problem is that most controllers can't handle the input voltage and when you get above 48v, it's a little harder to find switches and breakers to handle the higher voltage.

If your panels do not have bypass diodes, you almost have to go parallel. With no bypass diodes, shade on just one panel will drop the output of your entire PV string to zero.
Please show me the efficiency curves that show the higher efficiency with higher voltage drop.

DC-DC converters are most efficient when input and output voltages are the same. The current is passed directly through. There is no boost or buck required. When buck or boost is required solid state devices go to work and generate heat.

The curves in my Epever manual show the efficiency at 33V input much better than at 66V. This makes sense when you think of the solid state devices gating back to drop the voltage. I'd guess most controllers are similar. See the upper curves on each of pages 21-24 in the following.

https://www.epsolarpv.com/upload/cer...MS-EL-V1.2.pdf

The Epever Tracer requires just one volt to use MPPT if I recall correctly. I think it's in the manual though I didn't find it in a quick scan.
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Old 08-05-2020, 09:25 PM   #18
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Please show me the efficiency curves that show the higher efficiency with higher voltage drop.

DC-DC converters are most efficient when input and output voltages are the same. The current is passed directly through. There is no boost or buck required. When buck or boost is required solid state devices go to work and generate heat.

The curves in my Epever manual show the efficiency at 33V input much better than at 66V. This makes sense when you think of the solid state devices gating back to drop the voltage. I'd guess most controllers are similar. See the upper curves on each of pages 21-24 in the following.

https://www.epsolarpv.com/upload/cer...MS-EL-V1.2.pdf

The Epever Tracer requires just one volt to use MPPT if I recall correctly. I think it's in the manual though I didn't find it in a quick scan.
May be why I wouldn't want to use an Epever on my trailer. I do use them for less expensive applications like trickle charging my boat or truck.
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Old 08-05-2020, 10:34 PM   #19
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May be why I wouldn't want to use an Epever on my trailer. I do use them for less expensive applications like trickle charging my boat or truck.
Why, what have you read/seen?

The Epever seem a bit heavy though I've not compared them to Victron. A lot of the weight is in the large cast aluminum heatsink. Victron controllers are likely all lighter.

No fan. A massive heat sink that never gets warm. I like that. Some Victron's have fans, some don't. None have much of a heat sink.

Will Prowse got one thing right when he endorsed the Epever .. the industrial terminals. Massive and secure. He didn't like the others.

I like having the monitor/setting screen on a wall inside the RV and the controller in the battery room.

Epever BN series that I have need 2 volts above battery voltage to go into MPPT mode. They can bring array voltage even closer to battery voltage to maximize power.

https://www.epsolarpv.com/upload/cer...-tracer-BN.pdf

https://smile.amazon.com/EPEVER-Cont...6684074&sr=8-5

Re victron efficiency .....

93% See page 24 near top of the chart.

https://www.victronenergy.com/upload...IT-PT-(A4).pdf

"up to 95%" see page 5
93-95% see page 28

https://www.victronenergy.com/upload...IT-PT-(A4).pdf

I thought there were other models, but the above are what I found on their manuals page.

I find no information re Victron's efficiency relative to input voltage.

It looks like the Epever wins hands down on efficiency at around 33V. Up at 66V it's a closer race but Epever wins.

Did I say I like having no fans ..............
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Old 08-05-2020, 11:16 PM   #20
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Victron that I have is 98%

100/50

Epever have Bluetooth?
Able to share voltage with the battery monitor do you have remote voltage sensing?

There is a reason the epever has a large heat sink....it needs it because of its low efficiency.

For a cheap Chinese controller, they aren't bad. I own two for use as trickle chargers.

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Why, what have you read/seen?

The Epever seem a bit heavy though I've not compared them to Victron. A lot of the weight is in the large cast aluminum heatsink. Victron controllers are likely all lighter.

No fan. A massive heat sink that never gets warm. I like that. Some Victron's have fans, some don't. None have much of a heat sink.

Will Prowse got one thing right when he endorsed the Epever .. the industrial terminals. Massive and secure. He didn't like the others.

I like having the monitor/setting screen on a wall inside the RV and the controller in the battery room.

Epever BN series that I have need 2 volts above battery voltage to go into MPPT mode. They can bring array voltage even closer to battery voltage to maximize power.

https://www.epsolarpv.com/upload/cer...-tracer-BN.pdf

https://smile.amazon.com/EPEVER-Cont...6684074&sr=8-5

Re victron efficiency .....

93% See page 24 near top of the chart.

https://www.victronenergy.com/upload...IT-PT-(A4).pdf

"up to 95%" see page 5
93-95% see page 28

https://www.victronenergy.com/upload...IT-PT-(A4).pdf

I thought there were other models, but the above are what I found on their manuals page.

I find no information re Victron's efficiency relative to input voltage.

It looks like the Epever wins hands down on efficiency at around 33V. Up at 66V it's a closer race but Epever wins.

Did I say I like having no fans ..............
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